1. Field of the Disclosure
The disclosure relates generally to resonator-based devices and, more particularly, to resonator-based clocks and other timing signal applications.
2. Brief Description of Related Technology
Accuracy measured in parts per million (ppm) is often required to keep accurate time information for time-of-day and other real time clock applications. Real time clocks are used in a variety of contexts relying on accurate time information, such as watches, clocks, PCs, mobile phones, cameras, appliances, wireless communications devices, etc.
Conventional real time clock output signals are generated from the output of an accurate quartz crystal oscillator, which has been trimmed to have an accuracy within 10 ppm to the target frequency, often 32.768 kHz. The frequency variation over the operating temperatures of quartz crystal has a parabolic shape. This parabolic shape has provided temperature frequency variation to about 13 ppm over a temperature range of 0-50 degrees, but can vary substantially outside of that temperature range.
Recently, micro-mechanical or microelectromechanical (MEMS) resonators have shown promise as a replacement to quartz crystal oscillators. While MEMS devices have been shown to provide size and cost advantages as well as compatibility with standard silicon circuitry, prior attempts to trim the initial MEMS resonator frequency have often introduced complexities, thereby increasing manufacturing costs.
The resonant frequency of a MEMS resonator also varies with temperature. Without any compensation, the resonant frequency of a MEMS resonator typically varies with temperature to an extent greater than that of a quartz crystal. Unfortunately, attempts to control or prevent temperature-based variation in the resonant frequency have often involved modifications to the MEMS resonator design.